A detailed genetic map of the terminus region of the chromosome of Escherichia coli is being constructed. This map will contain the loci previously known to be in the vicinity of the terminus region, and it will also include drug resistance transposons that have been inserted in this region. The genetic map obtained by P1 transduction will be compared with that obtained by conjugation to determine where chromosome transfer is inhibited. The loci will also be used to determine precisely where DNA synthesis is inhibited during the replication cycle. This will be determined by DNA-DNA hybridization, using various loci that have been cloned. A restriction map of the terminus region is also being constructed. Prophage have been inserted into the terminus region, and the chromosomal DNA that is replicated after induction of the prophage is used for the restriction analysis.